Well, actually I have the same problem.
I'd like to burn the new solydk201901 64 bit ISO, but no devices are listed in the window.
I formatted the usb-stick too but no chance to burn it. The field always remains grey and does not offer any option. Refresh device list has no effect.

I used to burn thanks to Solydxk USB-Creator without problems, using the same USB stick.

Since now it doesn't work I have burned it successfully with Linux Mint.